1. Field of the Invention
This invention relates to an internal combustion engine provided with an auxiliary combustion chamber in communication with the main combustion chamber through a nozzle, and more particularly to such internal combustion engine wherein the fuel-air mixture burned in the auxiliary combustion chamber is provided from the main combustion chamber.
2. Description Of The Prior Art
As a measure for cleaning the exhaust gas released from an internal combustion engine, methods were proposed in which generation of harmful gas components is suppressed. According to these methods, the mixture supplied into the combustion chamber in the engine is considerably reduced in concentration to minimize formation of unburned gases.
These methods, however, had the problems of deteriorated ignitability and poorer engine efficiency and also it was necessary to advance the ignition time enough to cover up retarded burning velocity resulting from the use of a lean mixture. As a solution to this problem, it was proposed to provide an auxiliary combustion chamber in communication with the main combustion chamber through a passage, and to dispose a spark plug in said auxiliary combustion chamber, thereby to improve ignitability and to increase burning velocity to obtain stabilized combustion for the engine using a lean mixture. According to this system, the mixture introduced into the main combustion chamber by the suction stroke of the engine flows into the auxiliary combustion chamber from said main combustion chamber through the passage with ascending movement of the piston in the compression stroke and is ignited by the spark plug provided in the auxiliary combustion chamber. As the mixture in the auxiliary combustion chamber is burned, the pressure in said chamber is elevated and the flame propagates into the main combustion chamber to stir up and rapidly burn the mixture staying therein. As a result, the burning condition is improved to prevent engine knock and ensure perfect combustion. Also, the mixture staying in the quenched portion in the main combustion chamber, where flame propagation is retarded, is efficiently burned to improve the operating performance of the engine while at the same time preventing the generation of unburned gases.
In such internal combustion engine, however, since the discharging gap of the spark plug is located in the auxiliary combustion chamber, that is, at a position spaced from the passage where gas velocity is high, the burned gas resulting from the mixture, after being ignited by the spark plug and burned during the working stroke of the engine, stagnates around the igniting portion of the spark plug, that is, in the vicinity of the discharging gap. The residual burned gas staying near the discharging gap is not entirely removed away even after the successive suction and compression strokes, and such gas excessively worsens the ignitability of the mixture. As a result, the engine tends to misfire in light-load or low-speed running to cause increased discharge of hydrocarbons, an unburned harmful component, and reduced engine performance.
One approach to the solution of this problem is a so-called stratified combustion type engine. In this type of engine, the easily ignitable rich mixture is supplied into the auxiliary combustion chamber and is ignited by the spark plug and burned, and the produced combustion gas is injected into the main combustion chamber through a passage to ignite and burn the lean mixture in the main combustion chamber. According to this system, however, since the mixture concentrations, or air-fuel ratios, in the main and auxiliary combustion chambers are different from each other, it is necessary to prepare two different types of mixture. Therefore, it is necessary to provide a fuel injection valve in the auxiliary combustion chamber or to provide an intake valve for supplying richer mixture into the auxiliary combustion chamber. Provision of such extra parts greatly complicates the mechanism of these fuel supply systems.